Implications of changes in the atmospheric circulation on the detection and attribution of regional surface air temperature trends

Qigang Wu, Univ. of Oklahoma, Norman, OK; and D. J. Karoly

Pervious studies have shown that observed surface air temperature (SAT) warming trends consistent with the response to anthropogenic forcing are detected at scales on the order of 500 km in many regions of the globe. However, the regional SAT trends projects strongly on the dominant natural atmospheric circulation modes, such as the Arctic Oscillation (AO), Antarctic Arctic Oscillation (AAO) and Cold Ocean-Warm Land (COWL)-like patterns. In the current couple models, the warming associate with the changes of atmospheric circulation is not well simulated. In this study we explore the influence of the exclusion of warming related to changes of the atmospheric circulation on the detection of a regional response to both anthropogenic and natural forcings. We compare observed SAT trends over three different periods in the 20th century with those simulated in responses to natural and anthropogenic forcings in a suite of five up-to-data coupled general circulation models. Control runs from four models are used to provide estimates of the internal variability of trends. We find that the detection and attribution of regional response to both anthropogenic and natural forcing is robust to this exclusion of warming related to changes of the atmospheric circulation considered here. .